Trundling along the streets of Boston, Staten Island, and Indianapolis in recent months, Google’s Street View cars haven’t just been collecting panoramic imagery. Fitted with methane sensors, the cars have also been sniffing out natural gas leaks, a hazard that affects many cities across the US and beyond. The Environmental Defense Fund linked up with Google Earth Outreach to conduct the pilot project, with three Street View cars gathering 15 million readings throughout the three locations. The initiative turned up “thousands” of leaks from utility pipes beneath the streets, providing officials with data on pollution “that used to be invisible,” EDF’s Fred Krupp wrote in a blog post Wednesday.